The objective of this study is to test the hypotheses that: 1) patients with IDDM have circadian changes in insulin sensitivity; 2) these changes are caused by circadian changes in hepatic glucose production and 3) that the circadian changes in hepatic glucose production can be altered with Metformin. The findings are likely to be of considerable clinical importance. Metformin is known to lower blood glucose by suppressing HGP. We hypothesize that it will be able to inhibit circadian nocturnal HGP and improve/facilitate glycemic control.